strace.c: refactor trace into two functions
This change decouples waiting for next event from reacting to it. This makes the control flow easier to understand, and serves as a preparation for implementing a pull-style API for LuaJIT. * strace.c (enum trace_event): New enum. (trace): Split into ... (next_event, dispatch_event): ... new functions. (main): Use them.
This commit is contained in:
Victor Krapivensky
parent
a25d7521ef
commit
6b4efe9f01
386
strace.c
386
strace.c
@ -2252,21 +2252,77 @@ print_event_exit(struct tcb *tcp)
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line_ended();
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}
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/* Returns true iff the main trace loop has to continue. */
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static bool
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trace(void)
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enum trace_event {
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/* Break the main loop. */
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TE_BREAK,
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/* Call next_event() again. */
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TE_NEXT,
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/* Restart the tracee with signal 0 and call next_event() again. */
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TE_RESTART,
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/*
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* For all the events below, current_tcp is set to current tracee's
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* tcb. All the suggested actions imply that you want to continue
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* tracing of the current tracee; alternatively, you can detach it.
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*/
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/*
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* Syscall entry or exit.
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* Restart the tracee with signal 0, or with an injected signal number.
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*/
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TE_SYSCALL_STOP,
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/*
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* Tracee received signal with number WSTOPSIG(*pstatus); signal info
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* is written to *si. Restart the tracee (with that signal number
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* if you want to deliver it).
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*/
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TE_SIGNAL_DELIVERY_STOP,
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/*
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* Tracee was killed by a signal with number WTERMSIG(*pstatus).
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*/
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TE_SIGNALLED,
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/*
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* Tracee was stopped by a signal with number WSTOPSIG(*pstatus).
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* Restart the tracee with that signal number.
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*/
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TE_GROUP_STOP,
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/*
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* Tracee exited with status WEXITSTATUS(*pstatus).
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*/
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TE_EXITED,
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/*
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* Tracee is going to perform execve().
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* Restart the tracee with signal 0.
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*/
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TE_STOP_BEFORE_EXECVE,
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/*
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* Tracee is going to terminate.
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* Restart the tracee with signal 0.
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*/
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TE_STOP_BEFORE_EXIT,
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};
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static enum trace_event
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next_event(int *pstatus, siginfo_t *si)
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{
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int pid;
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int wait_errno;
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int status;
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bool stopped;
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unsigned int sig;
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unsigned int event;
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struct tcb *tcp;
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struct rusage ru;
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if (interrupted)
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return false;
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return TE_BREAK;
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/*
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* Used to exit simply when nprocs hits zero, but in this testcase:
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@ -2286,21 +2342,21 @@ trace(void)
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* on exit. Oh well...
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*/
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if (nprocs == 0)
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return false;
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return TE_BREAK;
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}
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if (interactive)
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sigprocmask(SIG_SETMASK, &start_set, NULL);
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pid = wait4(-1, &status, __WALL, (cflag ? &ru : NULL));
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pid = wait4(-1, pstatus, __WALL, (cflag ? &ru : NULL));
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wait_errno = errno;
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if (interactive)
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sigprocmask(SIG_SETMASK, &blocked_set, NULL);
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if (pid < 0) {
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if (wait_errno == EINTR)
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return true;
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return TE_NEXT;
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if (nprocs == 0 && wait_errno == ECHILD)
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return false;
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return TE_BREAK;
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/*
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* If nprocs > 0, ECHILD is not expected,
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* treat it as any other error here:
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@ -2309,10 +2365,12 @@ trace(void)
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perror_msg_and_die("wait4(__WALL)");
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}
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status = *pstatus;
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if (pid == popen_pid) {
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if (!WIFSTOPPED(status))
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popen_pid = 0;
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return true;
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return TE_NEXT;
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}
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if (debug_flag)
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@ -2324,14 +2382,161 @@ trace(void)
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if (!tcp) {
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tcp = maybe_allocate_tcb(pid, status);
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if (!tcp)
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return true;
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return TE_NEXT;
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}
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clear_regs();
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event = (unsigned int) status >> 16;
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if (event == PTRACE_EVENT_EXEC) {
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/* Set current output file */
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current_tcp = tcp;
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if (event == PTRACE_EVENT_EXEC)
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return TE_STOP_BEFORE_EXECVE;
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if (cflag) {
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tv_sub(&tcp->dtime, &ru.ru_stime, &tcp->stime);
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tcp->stime = ru.ru_stime;
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}
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if (WIFSIGNALED(status))
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return TE_SIGNALLED;
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if (WIFEXITED(status))
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return TE_EXITED;
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if (!WIFSTOPPED(status)) {
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/*
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* Neither signalled, exited or stopped.
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* How could that be?
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*/
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error_msg("pid %u not stopped!", pid);
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droptcb(tcp);
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return TE_NEXT;
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}
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/* Is this the very first time we see this tracee stopped? */
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if (tcp->flags & TCB_STARTUP)
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startup_tcb(tcp);
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sig = WSTOPSIG(status);
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switch (event) {
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case 0:
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/*
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* Is this post-attach SIGSTOP?
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* Interestingly, the process may stop
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* with STOPSIG equal to some other signal
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* than SIGSTOP if we happend to attach
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* just before the process takes a signal.
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*/
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if (sig == SIGSTOP && (tcp->flags & TCB_IGNORE_ONE_SIGSTOP)) {
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if (debug_flag)
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error_msg("ignored SIGSTOP on pid %d", tcp->pid);
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tcp->flags &= ~TCB_IGNORE_ONE_SIGSTOP;
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return TE_RESTART;
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} else if (sig == syscall_trap_sig) {
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return TE_SYSCALL_STOP;
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} else {
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*si = (siginfo_t) {};
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/*
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* True if tracee is stopped by signal
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* (as opposed to "tracee received signal").
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* TODO: shouldn't we check for errno == EINVAL too?
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* We can get ESRCH instead, you know...
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*/
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bool stopped = ptrace(PTRACE_GETSIGINFO, pid, 0, si) < 0;
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return stopped ? TE_GROUP_STOP : TE_SIGNAL_DELIVERY_STOP;
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}
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break;
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#if USE_SEIZE
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case PTRACE_EVENT_STOP:
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/*
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* PTRACE_INTERRUPT-stop or group-stop.
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* PTRACE_INTERRUPT-stop has sig == SIGTRAP here.
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*/
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switch (sig) {
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case SIGSTOP:
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case SIGTSTP:
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case SIGTTIN:
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case SIGTTOU:
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return TE_GROUP_STOP;
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}
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return TE_RESTART;
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#endif
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case PTRACE_EVENT_EXIT:
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return TE_STOP_BEFORE_EXIT;
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default:
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return TE_RESTART;
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}
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}
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/* Returns true iff the main trace loop has to continue. */
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static bool
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dispatch_event(enum trace_event ret, int *pstatus, siginfo_t *si)
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{
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unsigned int restart_op = PTRACE_SYSCALL;
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unsigned int restart_sig = 0;
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switch (ret) {
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case TE_BREAK:
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return false;
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case TE_NEXT:
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return true;
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case TE_RESTART:
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break;
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case TE_SYSCALL_STOP:
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if (trace_syscall(current_tcp, &restart_sig) < 0) {
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/*
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* ptrace() failed in trace_syscall().
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* Likely a result of process disappearing mid-flight.
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* Observed case: exit_group() or SIGKILL terminating
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* all processes in thread group.
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* We assume that ptrace error was caused by process death.
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* We used to detach(current_tcp) here, but since we no
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* longer implement "detach before death" policy/hack,
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* we can let this process to report its death to us
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* normally, via WIFEXITED or WIFSIGNALED wait status.
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*/
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return true;
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}
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break;
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case TE_SIGNAL_DELIVERY_STOP:
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restart_sig = WSTOPSIG(*pstatus);
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print_stopped(current_tcp, si, restart_sig);
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break;
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case TE_SIGNALLED:
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print_signalled(current_tcp, current_tcp->pid, *pstatus);
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droptcb(current_tcp);
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return true;
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case TE_GROUP_STOP:
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restart_sig = WSTOPSIG(*pstatus);
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print_stopped(current_tcp, NULL, restart_sig);
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if (use_seize) {
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/*
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* This ends ptrace-stop, but does *not* end group-stop.
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* This makes stopping signals work properly on straced
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* process (that is, process really stops. It used to
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* continue to run).
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*/
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restart_op = PTRACE_LISTEN;
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restart_sig = 0;
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}
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break;
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case TE_EXITED:
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print_exited(current_tcp, current_tcp->pid, *pstatus);
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droptcb(current_tcp);
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return true;
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case TE_STOP_BEFORE_EXECVE:
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/*
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* Under Linux, execve changes pid to thread leader's pid,
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* and we see this changed pid on EVENT_EXEC and later,
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@ -2348,167 +2553,32 @@ trace(void)
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* On 2.6 and earlier, it can return garbage.
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*/
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if (os_release >= KERNEL_VERSION(3,0,0))
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tcp = maybe_switch_tcbs(tcp, pid);
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current_tcp = maybe_switch_tcbs(current_tcp, current_tcp->pid);
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if (detach_on_execve) {
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if (tcp->flags & TCB_SKIP_DETACH_ON_FIRST_EXEC) {
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tcp->flags &= ~TCB_SKIP_DETACH_ON_FIRST_EXEC;
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if (current_tcp->flags & TCB_SKIP_DETACH_ON_FIRST_EXEC) {
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current_tcp->flags &= ~TCB_SKIP_DETACH_ON_FIRST_EXEC;
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} else {
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detach(tcp); /* do "-b execve" thingy */
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detach(current_tcp); /* do "-b execve" thingy */
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return true;
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}
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}
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}
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break;
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/* Set current output file */
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current_tcp = tcp;
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if (cflag) {
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tv_sub(&tcp->dtime, &ru.ru_stime, &tcp->stime);
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tcp->stime = ru.ru_stime;
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}
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if (WIFSIGNALED(status)) {
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print_signalled(tcp, pid, status);
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droptcb(tcp);
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return true;
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}
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if (WIFEXITED(status)) {
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print_exited(tcp, pid, status);
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droptcb(tcp);
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return true;
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}
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if (!WIFSTOPPED(status)) {
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/*
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* Neither signalled, exited or stopped.
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* How could that be?
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*/
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error_msg("pid %u not stopped!", pid);
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droptcb(tcp);
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return true;
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}
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/* Is this the very first time we see this tracee stopped? */
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if (tcp->flags & TCB_STARTUP) {
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startup_tcb(tcp);
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}
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sig = WSTOPSIG(status);
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switch (event) {
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case 0:
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break;
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case PTRACE_EVENT_EXIT:
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print_event_exit(tcp);
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goto restart_tracee_with_sig_0;
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#if USE_SEIZE
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case PTRACE_EVENT_STOP:
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/*
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* PTRACE_INTERRUPT-stop or group-stop.
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* PTRACE_INTERRUPT-stop has sig == SIGTRAP here.
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*/
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switch (sig) {
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case SIGSTOP:
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case SIGTSTP:
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case SIGTTIN:
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case SIGTTOU:
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stopped = true;
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goto show_stopsig;
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}
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/* fall through */
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#endif
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default:
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goto restart_tracee_with_sig_0;
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}
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/*
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* Is this post-attach SIGSTOP?
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* Interestingly, the process may stop
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* with STOPSIG equal to some other signal
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* than SIGSTOP if we happend to attach
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* just before the process takes a signal.
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*/
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if (sig == SIGSTOP && (tcp->flags & TCB_IGNORE_ONE_SIGSTOP)) {
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if (debug_flag)
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error_msg("ignored SIGSTOP on pid %d", tcp->pid);
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tcp->flags &= ~TCB_IGNORE_ONE_SIGSTOP;
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goto restart_tracee_with_sig_0;
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}
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if (sig != syscall_trap_sig) {
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siginfo_t si = {};
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/*
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* True if tracee is stopped by signal
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* (as opposed to "tracee received signal").
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* TODO: shouldn't we check for errno == EINVAL too?
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* We can get ESRCH instead, you know...
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*/
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stopped = ptrace(PTRACE_GETSIGINFO, pid, 0, &si) < 0;
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#if USE_SEIZE
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show_stopsig:
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#endif
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print_stopped(tcp, stopped ? NULL : &si, sig);
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if (!stopped)
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/* It's signal-delivery-stop. Inject the signal */
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goto restart_tracee;
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/* It's group-stop */
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if (use_seize) {
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/*
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* This ends ptrace-stop, but does *not* end group-stop.
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* This makes stopping signals work properly on straced process
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* (that is, process really stops. It used to continue to run).
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*/
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if (ptrace_restart(PTRACE_LISTEN, tcp, 0) < 0) {
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/* Note: ptrace_restart emitted error message */
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exit_code = 1;
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return false;
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}
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return true;
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}
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/* We don't have PTRACE_LISTEN support... */
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goto restart_tracee;
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case TE_STOP_BEFORE_EXIT:
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print_event_exit(current_tcp);
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break;
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}
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/* We handled quick cases, we are permitted to interrupt now. */
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if (interrupted)
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return false;
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/*
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* This should be syscall entry or exit.
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* Handle it.
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*/
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sig = 0;
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if (trace_syscall(tcp, &sig) < 0) {
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/*
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* ptrace() failed in trace_syscall().
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* Likely a result of process disappearing mid-flight.
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* Observed case: exit_group() or SIGKILL terminating
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* all processes in thread group.
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* We assume that ptrace error was caused by process death.
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* We used to detach(tcp) here, but since we no longer
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* implement "detach before death" policy/hack,
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* we can let this process to report its death to us
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* normally, via WIFEXITED or WIFSIGNALED wait status.
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*/
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return true;
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}
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goto restart_tracee;
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restart_tracee_with_sig_0:
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sig = 0;
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restart_tracee:
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if (ptrace_restart(PTRACE_SYSCALL, tcp, sig) < 0) {
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if (ptrace_restart(restart_op, current_tcp, restart_sig) < 0) {
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/* Note: ptrace_restart emitted error message */
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exit_code = 1;
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return false;
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}
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return true;
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}
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@ -2523,7 +2593,9 @@ main(int argc, char *argv[])
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exit_code = !nprocs;
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while (trace())
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int status;
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siginfo_t si;
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while (dispatch_event(next_event(&status, &si), &status, &si))
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;
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cleanup();
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